The Earth got used up. We found a new solar system and used terraforming technology to create hundreds of new Earths. The central planets formed the Alliance and decided that all worlds should unite under their rule. There was some disagreement on that point.

After the War for Unification, many Independents–those who fought and lost–drifted to the edges of the system, far from Alliance control. Out on the Rim, people struggle to get by with the most basic technologies. Out here a ship will bring you work. A gun will help you keep it.